worker: fixed infinite loop on send failure

The problem here is when qr_task_send() returns an error, the
following error handler will attempt to cancel all tasks that were
started on the same connection, but that will only work for the first
task (which is finished), the qr_task_on_send() will have no effect
on tasks in progress as the passed handle is NULL, and the task->finished
is false, thus looping infinitely.

The solution here is to let the rest of the tasks complete, even though
sending answer back will fail (which is fine).
19 jobs for marek/fix-infinite-loop-on-send-error in 13 minutes and 5 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #130077
docker linux amd64
build:clang:linux:amd64

00:00:39

passed #130076
docker linux amd64
build:linux:amd64

00:00:38

passed #130078
docker linux amd64
srpm

00:00:25

 
  Test
passed #130094
docker linux amd64
deckard:linux:amd64

00:06:54

passed #130092
privileged
distro:epel-7

00:03:38

passed #130091
privileged
distro:fedora-27

00:04:12

passed #130084
docker
doc

00:01:04

passed #130083
docker linux amd64
installcheck:linux:amd64

00:01:18

passed #130086
docker linux amd64
installcheck:valgrind:linux:amd64

00:02:04

passed #130080
docker
lint:c

00:02:45

failed #130081
docker allowed to fail
lint:clang-scan-build

00:01:31

passed #130079
docker
lint:lua

00:00:44

passed #130089
docker linux amd64
respdiff:iter:tcp:linux:amd64

00:02:11

passed #130090
docker linux amd64
respdiff:iter:tls:linux:amd64

00:02:17

passed #130088
docker linux amd64
respdiff:iter:udp:linux:amd64

00:02:55

passed #130082
docker linux amd64
test:linux:amd64

00:01:45

passed #130087
docker linux amd64
test:linux:amd64:valgrind

00:01:43

failed #130085
docker linux amd64
deckard:linux:amd64

00:01:21

 
  Coverage
passed #130093
docker linux amd64
coverage

00:00:26

71.7%
 
Name Stage Failure
failed
lint:clang-scan-build Test
                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5 warnings generated.
CCLD daemon/kresd
scan-build: 28 bugs found.
scan-build: Run 'scan-view /builds/knot/knot-resolver/scan-results/2018-04-14-042402-13-1' to examine bug reports.
Uploading artifacts...
scan-results: found 33 matching files
Uploading artifacts to coordinator... ok
id=130081 responseStatus=201 Created token=Wb6Y8A3W
ERROR: Job failed: exit code 1